Circuit arrangements for converting an alternating voltage into a rectified voltage are frequently used in battery charging devices. Chargers of this type are provided, for instance, for charging the batteries integrated into devices used for mobile communications or digital cameras. Chargers are, furthermore, used to charge a single battery or multiple batteries.
Circuit arrangements for converting an alternating voltage into a rectified voltage are also used in mains power supply plugs. Mains power supply plugs are used for devices that can be connected to the mains electrical supply network, but which do not operate internally from a mains voltage of 230 V, but from a smaller, rectified voltage. Usual circuit arrangements for converting an alternating voltage into a rectified voltage are, typically, a half-wave rectifier or a bridge rectifier.
FIGS. 1A and 1B show typical circuit arrangements for converting an alternating voltage into a rectified voltage. Components that have the same effect or function are given the same reference codes.
FIG. 1A illustrates a typical half-wave rectifier, comprising a diode 11. At its input, the circuit arrangement is connected to a transformer 4 that serves to transform the mains voltage into what is usually a lower magnitude of alternating voltage U-IN, and/or for electrical isolation. One terminal of the diode 11 is connected to the alternating voltage U-IN. At its output, the diode 11 provides a rectified voltage U-OUT. The rectified voltage U-OUT can be passed to an electrical load 7 comprising a capacitor 9.
A current then flows through the diode 11 when the instantaneous value of the alternating voltage U-IN is greater than a threshold voltage for the diode, and the instantaneous value of the rectified voltage is U-OUT. Depending on the exact type, the threshold voltage of the diode can, for instance, be of the order of 0.3 V to 0.6 V. This means that less than a complete half-wave of the alternating voltage U-IN is used for conversion into the rectified voltage U-OUT.
FIG. 1B illustrates a typical bridge rectifier, comprising four diodes 11, 12, 13, 14. A battery 10 is coupled via a charging circuit 15 to the output terminal 5. In this circuit arrangement, segments of both half-waves of the alternating voltage U-IN are exploited to generate the rectified voltage U-OUT.
In usual circuit arrangements it is not possible to exploit the full alternating voltage U-IN to generate the rectified voltage U-OUT due to the barrier or forward threshold voltage exhibited by diodes. The rectified voltage U-OUT is, even in the absence of a load, always one diode forward-bias voltage less than the peak value of the alternating voltage U-IN.